Internal-combustion heater with air-cooled muffler



p 1949. H. J. DE N. McCOLLUM 2,482,987

INTERNAL-COIBUSTION HEATER VIITH.AIR'-COOLD IUFFLER r1104 Jun. 5, 1943 ashuts-sheet 1 Sept. 27, 1949. .11. J. as N. M coLLuM 2,482,987

IITBRNAL-COIBUSTION HEATER WITH AIR-COOLBD MUFFLER l'ilod Juno 5, 19$ 9Sheets-Sheet 2 Sept. 27, 1949. H. 4. DE N. M coLLuM 2,432,987

INTERNALCOIBUSTION HEATER WITH AIR-COOLED IUFFLE R Filed Juno 5, 1943 9Sheets-Sheet 3 Sept. 27, 1949. H. J. DE N. M coLLuM 2,482,987

INTERNAL-COMBUSTION- HEATER, w-r'rn AIR-COOLBD MUFFLER Filed Jun. 5;1943 9 Shee'ts-Sheet 5 Sept. 27, 1.949. H. J. as N. M COLLUM 2,482,937

INTERNAL-COIQUSTION HEATER WITH AIR-COOLBD IUFPLBR Filed m. s. 194: 9Sheath-Shoat s @Zkmz M.

p 1949- 'H. .J- m: N M coLLuM 2,482,987

, INTERNAL-COMBUSTION HEATER WITH AIR-000L313 IUPPLBR Filed June 5, 19439 Sheets-Sheet 7 Se t. 27, 1949. H. J. DE N. M coLLuM 2,432,987

INTERNAL-COIBU'l-ION HEATER WITH AIR-COOLBD IUFFLER Filqd Jun 5, 1943 9Shots-Shoot 8 Se t. 27, 1949. H. m a. M C OLLUM 2,482,987

INTERNAL-COMBUSTION HEATER WITH MR-COOLED IUFFIJER Filed Juno 5.. 1943 sslmu-shuz 9 filmy/Ear?- L @rjfiPlfDi/cf/Zmn Patented Sept. 27, 1949INTERNAL-COMBUSTION HEATER WITH AIR-COOLED MUFFLER Henry J. De N.McCollum, Chicago, 111.; Thelma McCollum, executrix of said Henry J.DeN. McCollum, deceased, assignor to Stewart-Warner Corporation,Chicago, 111., a corporation of Virginia Application June 5, 1943,Serial No. 489.7

26 Claims. (01. 128-116) Another object of my invention is to provide aheater havingnew and improved means for preventing the accumulation ofcombustible mixture in the muflier.

Another object of my invention is to provide a heater having an improvedmeans for cooling the exhaust gases.

Another object of my invention is to provide a heater having new andimproved means for introducing secondary air into the hot products ofcombustion.

Another'object of my invention is to provide a heater havinga new andimproved arrangement for preheating air utilized for combustionpurposes.

Another object of my invention is to provide a heater having new andimproved heat exchange means for heating the ventilating air.

Another object of my invention is to provide a heater having a lessexpensive and lighter weight muiller than those heretofore used.

Another object of my invention is to provide a heater having novel meansfor introducing secondary air into the products of combustion and forpreventing products of combustion from entering the ventilating air.

Another object of my invention is to provide a new and improved heaterwhich offers minimum resistance to gas and air flow therethrough.

Another object of my invention is to provide a new and improved heaterwhich may be easily disassembled and re-assembled for inspection,repair, cleaning, or other similar purposes.

Another object of my invention is to provide a heater having theforegoing advantages and which is inexpensive to manufacture and capableof affording long and trouble-free service.

Other objects and advantages will become apparent as the descriptionproceeds.

In the drawings:

Fig. 1 is a longitudinal, sectional view through a preferred embodiment01' my invention;

Fig. 2 is a transverse, sectional view taken on the line 2-2 of Fig. 1;

Fig. 3 is a partial, transverse, sectional view taken on the line 3-3 ofFig. 1;

Fig. 4 is an irregular, transverse, sectional view taken on the net-4 ofFig. 1;

Fig. 5 is a longitudinal, sectional view through a modified form of myinvention;

Fig. 6 is a transverse, sectional view taken on the line 6-6 of F18. 5;

Fig. 7 is a partial, horizontal section taken on the line 1-1 of Fig. 5;

Fig. 8 is an irregular, generally horizontal, sectional view taken onthe line 8-! of Fig. 6;

Fig. 9 is an end view of the combustion chamber and associated parts andis taken in the plane of theline $401218. 7;

Fig. 10 is a longitudinal, sectional view of a further modification;

Fig. 11 is a longitudinal, sectional view of another modification;

Fig. 12 is a longitudinal, sectional view of another modification;

Fig. 13 is a longitudinal, sectional view of an other modification; and

Fig. 14 is a longitudinal, sectional view of another modification.

That embodiment of my invention which is shown in Figs. 1 to 5,inclusive, comprises a tubular casing 2|, having an inlet end 22 adaptedto be supplied with air by a ram, blower, or other suitable means. Theoutlet end 24 of the casing may discharge directly into an airplanecabin or other space to be heated, or may be connected to a duct systemleading to a plurality of outlets arranged at selected locations in thesame or diilerent spaces. Any suitable or usual means may be providedfor controlling communication between the ram and the casing 20 andbetween this casing and the space or spaces to be heated.

A combustion chamber 26 is located in the easing 2| adjacent the inletend 22 and has an end wall 28 and a cylindrical side wall, 30. A pipe 32is attached to the end wall 23 and extends through the center of thecombustion chamber in coaxial relationship to the cylindrical wall 30thereof. The lei'thand or inlet end of the pipe 30 is in opencommunication with the inlet end 22 of the casing II so that thecombustion chamber 26 is annular.

A carburetor 34 is shown as being provided for the purpose of supplyingcombustible mixture to the combustion chamber 2. A pipe 38 connects thecarburetor ll with any suitable source of fuel and one or more nozzles38 deliver this fuel into the throat of a Venturitube 40 which forms apart of the carburetor 34. The lefthand or outlet end of the Venturitube 46 is connected to one end of an induction pipe 42 which extendsthrough the casing 26 and an opening 44 in the wall 36 of the combustionchamber and has a curved end 46 lying closely adjacent this wall. Thisend 46 is exposed to the heat of the combustion chamber and serves topreheat to the desired extent the combustible mixture being delivered tothis chamber by way of the induction tube 42. As best shown in Fig. 1,this end 46 is inclined toward the end wall 28 of the combustion chamberwhereby the combustible mixture is caused to whirl about the axis ofthis chamber adjacent the rear wall thereof and all fuel is completelyconsumed within this chamber.

As best shown in Fig. 2, a housing 48 is attached to the cylindricalwall 46 of the combustion chamber and provides a passageway 56 whichcommunicates with the combustion chamber by way of an inlet 52 and anoutlet 54. An igniter plug 56 is located in the passage 56 in spacedrelation to'the walls thereof so that combustible mixture may flowaround the plug 56 and be ignited by the electrical coil 56 in the lowerend thereof. In ordinary practice, the igniter plug 56 is automaticallydisconnected from its source of current when the heater attainsoperating temperature and one or more re-igniters 66 (Fig. 1) may beprovided to maintain combustion thereafter.

A ring 62 is attached to the cylindrical wall of the combustion chamberby welding, or in any other suitable manner, and serves to prevent theescape of liquid fuel from this chamber. The righthand end of thecylindrical wall 36 is provided with a flange 64 which is attached byscrews 66, Or in any other suitable manner, to supporting brackets 68and also to one end of a heat exchanger, indicated generally byreference numeral 16. Similar brackets I2 attach the other end of theheat exchanger to the casing 26, the brackets 68 and 12 being secured tothe casing by screws I4, or in any other suitable manner.

The heat exchanger 16 comprises a sheet metal generally cylindricalshell I6 having its opposite ends welded or otherwise suitably securedto rings 18 and 86. The shell I6 is corrugated, as best shown in Fig. 3,and fins 62 have their bases secured in folds of the corrugated shellI6. The radially outward portions of the fins 82 project into theventilating air passage 84 formed between the casing 26 and the shellI6.

A mufiler indicated generally by a reference character 86 is located inthe heat exchanger I6 and has a cylindrical body 68 of sheet metal, orother suitable material, which cooperates with the shell I6 of the heatexchanger to form longi tudinally extending passages 66 for the hotproducts of combustion issuing from the combustion chamber 26. A sheetmetal cone 92 connects the lefthand end of muifler body 66 with pipe 32and serves to direct the hot gases issuing from the combustion chamberinto the lefthand ends of the gas passages 96. As the hot products ofcom bustion traverse these gas passages, heat is given up to the shellI6 and fins 62, which transmit this heat to ventilating air flowingthrough the ventilating air passage 64. The gases then pass into anoutlet chamber 84 and are discharged to atmosphere through outlet pipe86 and fitting 96 and any suitable exhaust pipe attached to the threadedend I66 of this fitting.

The outlet pipe 66 is attached to a plate I6I which closes the righthandend of the heat exchanger I6 and which is attached thereto by bolts I63,some of which also serve to attach this heat exchanger to bracket I2. Asbest shown in Fig. 1, the outlet pipe 96 is provided with a boss or footI65 which rests against the plate I6I at a special place provided byomitting one of the bolts I63. The pressure toot I65 forms an extrasupport for the outlet pipe 66 and gives this pipe and the fitting 66attached thereto additional stability.

The mufller 66 has an annular sound absorbing chamber I62, which isillustrated as being in communication with the gas passages 96 through asingle, annular row of openings I64 forming acoustic couplings betweenthe annular chamber I62 and the gas passages. As clearly shown in Fig.1, this single annular row of openings I64 is located adjacent theleithand end oi. the muiller 86 and serves to conduct sound into theannular chamber I62 where it is absorbed by the glass wool or stainlesssteel wool I66 located in this chamber.

The inner wall of the annular muiiier chamber I62 is formed by a tubeI66 supported in end walls I I6 and H2. The tube I66 is in axialalignment with the pipe 62 and is shown as being of the same size asthis pipe. The leithand end of the tube I66, however, is spaced from therighthand end of the pipe 62, so that air leaving the righthand end ofthe pipe 62 must pass through a conical chamber I I4 before entering thetube I66. This conical chamber H4 is formed by the cone 92 and end wallI I2 of the runner body and serves to prevent the wool in the lefthandend of the mumer from being overheated by the hot products of combustionissuing from the combustion chamber. The air passing from pipe 62 totube I68 absorbs heat from the walls 01' this chamber so that thischamber also serves to increase the preheating of the air entering thetube I66.

Most oi the air flowing through the tube I66 enters pipes II 6 and I I6leading to the air inlet of the carburetor 64. when the heater isoperating normally, the air delivered to the carburetor through thesepipes is preheated to'the desired temperature, and this preheatingmaterially im proves the operation of the heater by aiding in thevaporization of the fuel delivered by the jet 36. A small part of theair flowing through the tube I66, however, passes through the annularspace I26 formed between the righthand end of the tube I66 and theleithand end of pipe H6 and enters the outlet chambers 94 where it mixeswith, dilutes and cools the products 01' combustion discharged toatmosphere by ways oi pipe 96 and fitting I66. This arrangement fordiluting the exhaust is accomplished with very low pres sure drop andwithout requiring outside connecions.

The purpose in diluting the exhaust gases is primarily to preventexplosions when the heater is being started. In other words, the exhaustgases are diluted to such an extent that any mixture of fuel and airentering the exhaust pipe and discharged therefrom will not explode eventhough combustible mixture delivered to the combustion chamber passestherefrom to the exhaust outlet without being burned in the heateritself. The introduction of secondary air into the exhaust chamber 64also serves to muile the exhaust end of the heater and permits theacoustic couplings between the interior of the muiiier and the gaspassages to be confined to the combustion end 01' the heater, as clearlyshown in Pig. 1.

I wish to call particular attention to the fact that I have provided asimple and emcient arrangement whereby the combustion air is preheatedin such a way that it cools the muiller and serves to preventoverheating of any part of this muiller by the heat of the combustionchamber and the hot products issuing therefrom. These objects, togetherwith the dilution of the exhaust are accomplished by a simple structurewhich may be easily assembled and disassembled for inspection, cleaningor repair. This structure also offers minimum resistance to flow of airand gas therethrough and may be constructed of light weight but sturdyparts which are capable of withstanding rough usage and giving long andtrouble-free service. This heater is highly efficient and has a highheat output for a given size and weight and so is particularly adaptedfor use in airplanes wherein these factors are especially important,although it is to be understood that my heater is not limited to suchuse and is also adapted for other purposes.

In Figs. to 9, inclusive, I have shown a modified form of my inventionwherein the heater com-- prises a casing I30 having its inlet endattached I are located in the casingI30 and are supported therefrom bybrackets I38 and I40 attached by screws, or other suitable means, to thecasing, heat exchanger and combustion chamber. As in the previousembodiment, the screws I42 which attach the brackets I38 to thecombustion chamber and heat exchanger also serve to secure thecombustion chamber and heat exchanger to each other.

A combustion air tube I44 has its lefthand end secured to the end wallof the combustion chamber and is in open communication with the airinlet pipe I32. The righthand end of the tube I44 is in sealedengagement with the lefthand end of a pipe I48 which connects with anexternal pipe I48 (Fig. 8) leading to a carburetor I80. A fuel supplypipe I52 connects the carburetor I I50 with an suitable source of fueland this fuel is delivered to a jet I84 located in the restricted throatof the Venturl tube I88 forming part of the carburetor I80. A mixture offuel and-air is formed in the Venturl tube I58 and this mixture isdelivered to the combustion chamber I34 by way of induction tube I88,having an end I80 which extends through the casing I30 and side wall ofthe combustion chamber I34.

of combustion into the lefthand ends of the gas passages I10. Therighthand ends of these gas passages discharge the cooled gases into anoutlet chamber I18 formed between the end wall I80 of the muiller and aplate I82, which closes the righthand end of the heat exchanger. Thesegases are discharged to atmosphere through outlet pipe I84 and fittingI86 and any suitable exhaust pipe attached to the threaded end of thisfitting.

In this embodiment of my invention, the mufiier I12 has an annularchamber I88 formed between the tube I44 and the outer wall I14, but inthis embodiment of my invention this chamber is not filled with glasswool or stainless steel wool, or other sound absorbing material.Instead, the particular arrangement of the muiller and especially theflow of air therethrough are relied upon to absorb sound and preventrumbling or other noises in the heater. A single row of openings I90-provided in the tube I44 connects the annular chamber I88 of the muilierwith the air passageway'through the tube I44 and permits a. small amountof air to flow from the tube I44 into the annular space I88. Annularrows of openings I92 and I94 connect the annular space I88 with the gaspassages I10 and a third an- The openings m, 192,194 and I88 arepreferably of such size as to form acoustic couplings which connect theannular space with the air passage in the tube I44 and also with the gaspassages through the heater. A small amount of air flows into theannular space I88 through openings I90 and this air flows slowly throughthe lefthand end of the muffler chamber I88 and out of the openings I92,I94 and I88 to mix with the hot products of combustion. This airperforms several functions. It cools the lefthand end of the muiller andprevents this end from beingoverheated by the heat of the combustionchamber and the hot gases issuing therefrom. It also absorbs soundentering the muilier through the openings I92, I94 and I98 and Themixture delivered to the combustion chamber I34 by the induction tubeI88 is ignited by an electrical igniter I82 located in the bracketprovided by a housing I84 attached to the cylindrical wall of thecombustion chamber. The combustion chamber is provided with one or morereigniters I68 to maintain combustion after the igniter I62 has been cutout by the usual thermostatic switch. A ring I88 is welded or otherwisesecured to the cylindrical wall of the combustion eliminates rumblingand other noises. This air flow, together with the large annular spacepro vided by. the inuiller chamber I88, serves eiTectively to quiet theheater. This air also functions as secondary air to dilute and slightlyreduce the temperature of the gases entering the passages I10 andprevents the lefthand ends of these passages from being overheated bythe inflowing gases.- The flow of secondary air through the muillershell also prevents combustible gases from entering the chamber I88 whenthe heater is first turned on and before combustion occurs in thecombustion chamber.

All of the foregoing advantages are obtained with a very small flow. ofair from the tube I44 through the mufller and into the gas passages ofthe heater. The operation of this heater is exceedingly eflicient andthisefllciency is accomplished by a structure of minimum weight-since nosound absorbing material need be provided in the mufller chamber. Theelimination of this sound absorbing material has a further advantage inthat such sound absorbing material is a part of the heater which has theshortest life and which requires the most frequent attention andservice.

In Fig. 10, I have shown a form of my invention which is more nearly thembodiment of Figs. 1 to 4, inclusive. In the embodiment of Fig. 10, thecombustion chamber 2" and the heat exchanger 202 are attached to eachother and to brackets 204 by screws 2", or in any other suitable manner.The other end of the heat exchanger 202 is separated by brackets 2" andthe brackets 204 and 2" are attached to the heater casing 2lll by screws212. The lefthand or inlet end of the casing 210 is connected to an airinlet pipe 214 which may lead from a ram, blower, or other suitablesource of air supply. The righthand end of the casing 2| I, as in theprevious embodiments, delivers the hot air to the space or spaces to beheated.

The heat exchanger 202 may be identical with the heat exchangers of theprevious embodiments and a muffler 2l6 is located in this heat exchangerto cooperate therewith in the formation of the gas passages 2l8. A tube22l extends through the combustion chamber and muilier and has itslefthand end in open communication with the air inlet pipe 2. Therighthand end of this tube 220 is sealed to the lefthand end of a pipe222 which connects with a second pipe 224 leading to the air inlet ofthe usual carburetor 226. A fuel supply pipe 22! connects the carburetorwith any suitable source of fuel and an induction tube 230 conducts thecombustible mixture formed in the carburetor to the combustion chamber200.

The tube 220 forms the inner wall of an annular muiiier chamber 232which is filled with stainless steel wool or glass wool or othersuitable sound absorbing material. A single annular row of openings 234connects this annular chamber with the gas passages 2 l8 and is clearlyshown in the drawing. This annular row of openings is located adjacentthe leithand end of the annular mulller chamber.

The outer cylindrical wall 2" of the muiiler has a conical extension 230which serves to direct the hot products of combustion issuing from thecombustion chamber into the lefthand ends of the gas passages 2I8. Thisconical extension 23! forms a tapered annular chamber 240 surroundingthat portion of the tube 220 which is intermediate the combustionchamber 2 and the mufller 2I6. Annular rows of openings 242 and 244connect opposite ends of the chamber 24. with the interior of the tube22.. An annular member 246 is located in the tube 22. between theopenings 242 and 244 and serves to restrict the flow of air through thisportion of tube 22. sufiiciently to cause some of the air entering thelefthand end of this tube to pass through openings 242 into annular.chamber 24! and thence through openings 244 back into this tube. Thiscirculation of air through the chamber 2" cools the lefthand end of themumer 2l6 and also aids in preheating the combustion air delivered tothe carburetor 228. In this form of my invention, no secondary air isintroduced into the products of combustion and all air entering thelefthand end of the tube 220 is delivered to the carburetor 226.

The embodiment of Fig. 11 is generally similar v to that of Fig. 10, butshows a somewhat different The combustion chamber 250 and heat exchanger252 are secured to each other by screws 254, which also connect theseparts to brackets 25. The other end of the heat exchanger 252 issupported by similar brackets 25' and the brackets 258 and 258 aresecured to the casing 2 by screws 262. The lefthand end of the casing 2is connected to an air inlet tube 264 and the righthand end of thecasing discharges heated air to one or more spaces to be heated.

A mufller 266 is located in the heat exchanger 252 and has an outercylindrical wall 2" which cooperates with the heat exchanger 252 to formgas passages 210' therethrough. The wall 2" has a tapered lefthand end212 connected to the enlarged righthand end 214 of a pipe 218 whichextends through the combustion chamber 2" and whose lefthand end is inopen communication with the air inlet pipe 284. The inner wall of theannular mullier 266 is formed by a tube 210 in sealing engagement withend walls 2" and 2'2 an intermediate partitions 224, 2", 2" and 2, whichcooperate with the end walls and with each other to form compartments222, 294, 2, 298 and ill. A single annular row of openings "2 connectseach compartment with the gas passages 21l whereby sound may enter theseveral compartments and be absorbed by the glass wool or stainlesssteel wool or other sound absorbing material located therein.

A sheet metal cup 304 is located in thtapered end 212 of the wall 268.The openvend of this cup is closed by the end wall 2" of the munler anda single annular row of openings 3 forms the sole means of communicationbetween pipe 21 and tube 218. All air entering pipe 21 flows around thebase and side walls of cup "4 and passes through openings 3" into theinterior of this cup and thence into tube 21!. In passing around theoutside of cup 204, this air is preheated and serves to protect thelefthand end of the muffler against the heat or the combustion chamber250 and the hot gases issuing therefrom. This preheated air then flowsthrough tube 212 and pipes ill and 3" to carburetor 212, where acombustible mixture is formed which is delivered to the combustionchamber through induction tube 3 H. The usual igniter plug II andre-igniter II I are provided to initiate and maintain combustion of thismixture. A pipe 32. connects the carburetor with any suitable source offuel.

In the embodiment of Fig. 11, all air entering the pipe 216 is preheatedand delivered to the carburetor as combustion air. There is no provisionfor introducing secondary air into the products of combustion formed inthe combustion chamber. The combustion air is preheated to the desiredtemperature and this preheating is so accomplished that it serves toprotect the muffler against undue heat from the combustion chamber andhot products of combustion issuing therefrom. The mufller in this formof my invention is divided into a plurality of compartments arrangedlengthwise of the gas passages and connected thereto at intervalsthroughout their length.

In the embodiment of Fig. 12, the combustion chamber 350 and heatexchanger 352 are attached to each other and are suspended from thecasing 354 by brackets 356, as in the previous embodiments. The heatershown in this figure is similar to that shown in Fig. 11, except that adiii'erent type of muflier is used and the air which passes through thecombustion chamber and muilier is not directed to the carburetor but isdischarged to the end wall 888 of the combustion chamber and in opencommunication'with the air'inlet pipe 382. The opposite end of the pipe888 is enlarged, as indicated at 888, and is attached to the conical end888 of the outer cylindrical sheet metal wall 388 of the mumer 818,which is located within the heat exchanger 882. The inner. wall of theannular mufller is formed by a tube 812, which is secured to cylindricalwall888 by end walls 318 and 318. The elongated annular muffling chamberformed between the cylindrical wall 388. and tube 312 is preferablyfilled with stainlessfsteel wool or glass wool, as indicated in thedrawing. A single annular row of openings 318 forms acoustic couplingsbetween the elongated chamber of the muffler and the gas passages 388through which the hot products of combustion pass in flowing from thecombustion chamber 388 to outlet chamber, 882 from which these gases aredischarged to atmosphere by way of outlet pipe'388 and fitting 888 andany suitable exhaust pipe which may be connected thereto.

The tapered end 888 of the cylindrical muilier wall 388 forms an airchamber 888 interposed between the combustion chamber 888 and themuffler 318. A sheet metal cup 888 is located in this chamber and has asingle annular row of perforations 392 through which air must pass inflowing from the pipe 888 to the tube 812. This air flows around theoutside of the cup 888 andthen through openings 882 into the interiorthereof, absorbing heat from the pipe 888 and tapered end 388 andprotecting the adjacent end of the muffler against excessive heat. Thisheated air then flows through tube 812 and is discharged intotherighthand or outlet end of the casing 388.

Most of the air delivered to the heater by the pipe 382 which connectsthis heater with a ram, blower, or other air supply means, passesbetween the casing 388 and heat exchanger 882 and absorbs heat from thisheat exchanger. This heated air is then discharged from the rlghthandend of the heat exchanger into the righthand or outlet end of the casing388, where it mixes with air which has passed through the center of thecombustion chamber and the, center of the muifler by way of pipes 388,chamber 388, muiiler tube 312, and a pipe 888 which forms an extensionthereof and which is welded or otherwise maintained in sealingengagement with the closure plate 388 for the righthand end of the heatexchanger.

The carburetor 398 may be of any conventional.

or suitable type and is supplied with fuel through a fuel supply pipe888 which connects this carburetor with any suitable source of fuel.This carburetor is supplied with combustion air through a pipe 882 whoseinlet end 888 passes through the casing 888 and is located inside thiscasing adjacent but downstream from the righthand end of the heatexchanger. Air entering this pipe 882 has passed over the heat exchangeror through the passageway passing through the center of the combustionchamber and muffler and when the heater is in operation, has attained atemperature which facilitates vaporization of the fuel mixed therewithin the carburetor 338. An induction tube 888 extends generally parallelto and outside of the casing 888 and has an end 888 which through thecasing 888 and a wall of the combustion chamber 388 to deliver acombustible mixture to this combustion chamber. This mixture isoriginally ignited by an electrical igniter 8 and combustion ismaintained by one or more re-igniters 2 after the igniter 818 has beencut out by the usual-thermostatic switch.

In the heater of Fig. 12, all of the heated air is'used either forventilation or as combustion air delivered to the carburetor 338. Noneof this heated air is introduced as secondary air into the products ofcombustion. The arrangement I of Fig. 12 is preferableto that of Fig.11, where the amount of air necessary to cool the muffler isconsiderably greater than the quantity of combustion air required by thecarburetor. The somewhat simpler muiiler of Fig. 12 is satisfactory formost purposes, but the more complex and expensive muiller of Fig. 11 canbe substituted therefor, if required.

The heater shown in Fig. 13 is similar to Fig. 11 in that most of theair passing through the muffler is directed to the carburetor and usedas combustion air. The heater of Fig. 13 diifers from Fig. 11, however,in that Fig. 13 shows a different type of muiiler and part of the airdirected into the mufiler is introduced into the products of combustionas secondary air to aid in the reduction of noise.

In Fig. 13, the heater has a combustion chamber 858 attached to one endof a heat exchanger 882 and supported in a casing 888 by means ofbrackets 888 and 888. The lefthand or inlet end of the casing 888 isattached to an air supply pipe 888 connected with a ram, blower, orother suitable air supply means.

A muiller 882 is located in the heat exchanger 882 and comprises acylindrical wall 888 and end 812 which is welded or otherwise sealed tothe' muffler end wall 888. The cylindrical wall 888 of the mufller isprovided with an annular series of openings 818 adjacent the end wall888. These openings form acoustic couplings between the muillerchamberand the gas passages 818 in the heat exchanger 882. Theseopenings 818 also permit secondary air toflow into the passages 818 andmix with the products of combustion passing therethrough to aid inreducing noise.

A sheet metal baflie 818 is located in the muffler chamber and isattached to the end wall 888 by rivets 818, or in any other suitablemanner. This baille 818 causes the air entering the muiiler through pipe818 to flow in close contact with the end walls of this muffler and toprevent these walls from becoming overheated. The presence of the bafiie818 also facilitates flow of air through the openings 812 into the gaspassages 8 18.

Pipes 888 and 882 connect the righthand end of the muiller chamber withthe air inlet of a carburetor 888 which'is supplied with fuel from anysuitable source through a fuel supply pipe 838. An induction tube 888has its outlet end 898 located in the combustion chamber 888 anddelivers a combustible mixture of fuel and air to this chamber. Thismixture is initially ignited l 1 is cut out by the usual thermostaticswitch, combustion is maintained by one or more re-igniters Only a smallproportion oi the air delivered to the heater by air supply pipe Ill isrequired for combustion purposes, or as secondary air. Most of this airis heated by passing between the easing 454 and heat exchanger "1 and isdischarged from the righthand end of the casing 454 into one or morespaces to be heated. The products of combustion leave the righthand endsor the gas passages I to enter an outlet chamber 4", from which theyflow to atmosphere through outlet pipe 488 and outlet fitting III andany suitable exhaust pipe connected thereto.

As clearly shown in this figure, the pipe III which conducts heated airto the carburetor inlet is preferably formed of two sheet metal sections502 and 5M. The section I" has a pair of diametrically opposed flangesIll and the section 504 has a pair of diametrically opposed iianges 508,abutting flanges Ill and "I, being welded together to form the unitaryDlDe structure. The outlet pipe 49! is preferably of the sameconstruction and the pressure loot ill constitutes an extension of theinner flanges of two pipe sections.

In this figure, the combustion air is supplied by the same air supplypipe which furnishes the ventilating air to be discharged into the cabinor other space or spaces to be heated. In some installations it may beduirable to provide a separate source for the combustion air and in thisfigure the end wall ill or the combustion chamher 450 is provided with aring ill welded to this wall and provided with tapped holes ll, so thatassaosv walls andnnsorthisheatexchanger. 'lhecooled gases flow from therighthand ends of these as passages ill into an outlet chamber Ill andare discharged to atmosphere through outlet pipe i" and fitting I", andany suitable exhaust pipe attached to the threaded end 0! this nttlnz.In this heater, all or the air supplied by pipe passes around thecombustion chamber Ill and through the annular passage I between thecasing I24 and shell I42 0! the heat exchanger. This air absorbs heatirom the heat exchanger and passes from the righthand end of the heatexchanger into the outlet end or the casing.

A muiller, indicated generally by reierence numeral I, is located in theheat exchanger in and has a cylindrical side wall I and end walls "8 andI" towing a mulling chamber which communicates-with the gas passages I82through a single annular row of openings "2 located in the side wall 5adjacent the end wall I. This muiiler is exposed to the heat or thecombustion chamber and the hot gases issuing therefrom and I haveprovided means for cooling this muiller by introducing air thereinto.This cooling means comprises a pipe I, having an inlet end "0 located inthe outlet end of the casing!" and positioned to receive heated airdischarged from i the righthand end oi the heat exchanger. This aseparate air inlet pipe for the combustion air may be secured to thisend wall in sealed relation to the pipe 410 extending through thecombustion chamber. Where a separate source of air is provided forcombustion purposes, this separate source may be a ram, blower, or anyother suitable means. Certain of the other figures have identical meansfor attachment or aseparate air supply pipe for the combustion air.

The murder 2 is of simple construction and design and the muiiiingchamber requires no sound absorbing material, such as stainless steelwool, or glass wool. The sound absorbing qualities of the chamberitself, together with the flow of air therethrough which increases thesesound absorbing properties, is adequate to provide a quiet heater wheresome secondary air is discharged into the gases flowing through the gaspassages 416. In this particular embodiment of my invention, the weightand cost of the sound absorbing material are eliminated and since only avery small amount of air is introduced into the products of combustionas secondary air, the heater is highl eiiicient and has a high beatoutput for a given size and weight.

The heater of Fig. 14 has a somewhat diflerent arrangement forintroducing cooling air into the mumer. In this heater the combustionchamber 520 and heat exchanger I22 are supported in the cylindricalcasing 2| by brackets I28 and ill. The lefthand or inlet end of thecasing 524 is conneoted to the usual air supp y P pe "I and therighthand or outlet end or this casing discharges directly or indirectlyinto the space or spaces requiring heat.

The hot products of combustion flow from the ri hthand end of thecombustion chamber III into the lefthand ends 01' the gas passages 32 inpipe passes through the rear wall III of the munier and is inclineddownwardly so that its outlet end 558 is located closely adjacent to andsubstantially opposite the center of the end wall 5".

The ventilating air entering the muiler through pipe 5" serves toprevent overheating of any part of the muiiler 5 and a mall part of thisair passes through openings I52 into gas passages I32 and serves assecondar air which mixes with the products of combustion and tends toeliminate noise therefrom The end wall "I is the part of the mufllerwhich is most likely to become overheated and the pipe "4 is sopositioned and arranged that it discharges air directly against thiswall to prevent such overheating. Most oi the air entering the muiiierthrough pipe Ill is utilizedas combustlonairandpassestothecarburetor I"by way 01' pipes in and I". This air absorbs additional heat from thewalls of the muilier so that the combustion air reaching the carburetoris considerably hotter than the ventilating air passing from therkhthand end of the heater casing 524 into the airplane cabin or otherspace or spaces requiring heat. v

A fuel supply pipe I" connects the carburetor I with any suitable sourceor fuel and the mixture of fuel and air formed in this. carburetor isdelivered to the combustion chamber ill through an induction pipe "Ihaving an outlet end "I located in this chamber. The combustible mixturedelivered to the combustion chamber III is ignited by the usualelectrlcal'igniter I12 and after this igniter is cut out by the usualthermostatic switch, a re-igniter I," insures continued combustion ofthe inflowing fuel and air mixture. A ring "I prevents escape of liquidll fuel from the combustion chamber when the heater is first started.

The heater of Fig. 14 is particularly advantageous where it is desirableto have the combustion air supplied to the carburetor at a tempera- 7cture materially greater than that of the ventilating air leaving theheater. This heater also utilizes a muiiler oi simple construction whichrequires no sound absorbing material, such as stainless steel wool orglass wool, and is inexthe heat exchanger and give up their heat to theII p i and 8m inweight.

- 13 Rachel the embodiments herein shown and described, comprises asimple heater which may be" made of lightweight but strong and ruggedparts and which has a high heat output for a relatively small, compactandlightweight struc-' ture of high efllciency. In each of theseembodiments, special air circulating means is provided to prevent anypart of the mumer from becoming overheated so that the portion of themuiiler which is most exposed to the heat of the combustion chamber andthe gases issuing therefrom is protected against burning out and isafforded a life equivalent to that of the other parts of the heater.These advantages are accomplished in a heater which may be easilydisassembled and reassembled for purposes of inspection, cleaning andrepair and all parts of the heater are so designed that they may beeasily manufactured by conventional methods and equipment.

Because the heaters herein shown and described are compact and eflicientand have a high heat outputfor agiven weight, these heaters areparticularly adapted for heating the cabins and other spaces in anairplane. My novel heaters, however, are equally capable of use forother purposes. The particular heat exchanger shown herein is claimed inmy co pending application, Serial No. 464,451, filed November 4, 1942,now Patent No. 2,380,602 of July 31, 1945, and the various combustionchambers and other features not herein claimed are claimed in other co-pending a. A heater oi the class described, comprising a casing havingone end adapted to be connected to a source of air supply, means forminga combustion chamber located in said casing, a heat exchanger connectedto said combustion champrior applications.' Other forms of heatexchangers and combustion chambers could be used in lieu of those hereinshown and described and various other changes could be made withoutdeparting from the scope of my invention. In

fact my invention may be incorporated in numerous other forms andincludes all variations and modifications falling within the scope ofthe appended claims.

Iclaim:

1. A heater comprising a casing adapted to be connected with a source ofair supply, means forming a combustion chamber in said casing, a tubularheat exchanger in said casing connected to said combustion chamber andreceivingproducts of combustion therefrom, a mufller located in saidheat exchanger, said mui'iler including a muiliing chamber and meansacoustically coupling said chamber to said heat exchanger and combustionchamber for damping out incipient sound and pressure waves, and meansfor circulating part of the air supplied to said casing through saidmufller to prevent any part of said mufller from becoming overheated.

2. A heater of the class described, comprising a casing having one endadapted to be con nectedto a ram or other source of air supply, meansforming a combustion chamber located in i said casing, a heat exchangerof tubular conformation having one end attached to said combustionchamber, a sheet metal muilier located in said heat exchanger and havinga wall cooperating therewith to form gas passages for hot i products ofcombustion issuing from said combustion chamber, said muiller includinga'muffling chamber and means acoustically coupling said chamber to saidheat exchanger and combustion chamber for damping out incipient soundand pressure waves, means forming an air cham-. ber between said muiiierand combustion chamber, and means for creating air flow through said airchamber to protect said muiller against overheating.

ber and receiving hot products of combustion therefrom, a muiiierlocated in said heat exchanger, said mufller including a mui'ilingchamber and means acoustically coupling said chamber to said heatexchanger and combustion chamber for damping out incipient sound andpressure waves, means forming an air chamber between said mufller andcombustion chamber, means providing a passage for supplying air to saidchamber from said source, and an outlet passage for said chamberextending through said muiiler.

4. A heater of the class described, comprising a casing having one endadapted to be connected to a source of air supply, means forming acombustion chamber located in said casing, a heat exchanger connected tosaid combustion chamber and adapted to receive hot products ofcombustion therefrom, a mufiler located in said heat exchanger, saidmuflier including a mufliing chamber and means acoustically couplingsaid chamber to said heat exchanger and combustion chamber for dampingout incipient sound and pressure waves, means forming an air chamberbetween said muiiier and combustion chamber, and a pipe extendingthrough said combustion chamber and connecting said air chamber withsaid I source of air supply.

5. A heater of the class described, comprising a casing having one endadapted to be connected to a source of air supply, means forming a comaexchanger connected to said combustion chamber and adapted to receivehot products of combustion therefrom, a muiiier located in said heatexchanger, s'aid mufller including a muiiiing chamber andmeans-acoustically coupling said chamber to said heat exchangerandcombustion chamber for damping out incipient sound and pressurewaves, means forming an air chamber between said muiiier and combustionchamber, and means for creating'air flow through said air chamber toprotect said muiiier against overheating, said means comprising a pipeextending through said 'combustion chamber and a second pipe extendingthrough said mumer.

6. A heater comprising a cylindrical casing having one end adapted to beconnected with a source of air supply and a second end connected to oneor more spaces requiring heat, means forming a combustion chamberlocated in said metal mumer located in said tubular heat excasing inspaced relation to the walls thereof, a tubular heat exchanger in saidcasing, said heat exchanger having one end connected to said combustionchamber and re'ceivinghot products of combustion therefrom, acylindrical sheet changer and having one end adjacent said com bustionchamber, said mufiler including a muiiiing chamber and meansacoustically coupling said source of air supply and a second endconnected to one or more spaces requiring heat, means forming, acombustion chamber located in said casing 76 in spaced relation to thewalls thereof, a tubular chamber to said heat exchanger and combustion15 heat exchanger in said casing, said heat exchanger having one endconnected to said combustion chamber and receiving hot products oicombustion therefrom, a cylindrical sheet metal muiiier located in saidtubular heat exchanger and having one end adjacent said combustionchamber, means for circulating air adjacent said end oi the muiiler toprevent said end from becoming overheated, a carburetor for supplyingcombustible mixture to said combustion chamber, and means ior conductingsaid circulated air to said carburetor.

8. A heater of the class described, comprising a casing having one endadapted to be connected to a source of air, means forming a combustionchamber located in said casing, a heat exchanger connected to saidcombustion chamber and located in said casing and receiving hot productsof combustion from said combustion chamber, a muiiler located in saidheat exchanger, said mumer including a muflling chamber and meansacoustically coupling said chamber to said heat exchanger and combustionchamber for damping out incipient sound and pressure waves, meansproviding a conical air chamber interposed between said combustionchamber and said muiiler, and means for creating a circulation of airthrough said air chamber to prevent overheating of said muiiler.

9. A heater of the class described, comprising a casing having one endadapted to be connected to a source oi air, means forming a combustionchamber located in said casing, a heat exchanger located in said casingand connected to said combusticn chamber, a mufller located in said heatexchanger, said muiiler including a muming chamber and meansacoustically coupling said chamber to said heat exchanger and combustionchamber for damping out incipient sound and pressure waves, said mufllerand heat exchanger cooperating to provide passages for hot productsassaosv of combustion issuing from said combustion,

chamber, means providing a passageway extending through said combustionchamber and muiiier, means for supplying air to said passageway, saidpassageway being provided with openings for admitting air to saidmuiller, and means provided by said muilier for discharging said airinto said products of combustion adjacent said combustion chamber.

10. A heater of the class described, comprising a casing having an endadapted to be connected to a source of air supply, means forming acombustion chamber located in said casing, a tubular heat exchangerlocated in said casing and connected to said combustion chamber, atubular muiller located in said heat exchanger and cooperating therewithto provide passages for hot gases issuing from said combustion chamber,said mufller including a muiiling chamber and meansacoustically couplingsaid chamber to said heat exchanger and combustion chamber for dampingout incipient sound and pressure waves, means for directing air throughthe interior of said muh iler, and means for directing a small portionof said air through said muiiler and into said gas passage.

11. A heater of the class described, comprising a casing having one endadapted to be connected to a source of air supply, means'torming acombustion chamber located in said casing, a tubular heat exchangerhaving one end connected to said combustion chamber and receivingproducts of combustion therefrom, a pipe extending through saidcombustion chamber and heat exchanger,

16- means for supplying air to said pipe, a shell surrounding said pipeand cooperating therewith to provide a mulling chamber, said shellcooperating with said heat exchanger to form a passage for said productsof combustion, means providing openings connecting said pipe with saidchamber, and means providing openings connecting said chamber with saidgas passage, said muiiier including a muming chamber and meansacoustically coupling said chamber to said heat exchanger and combustionchamber ior damping out incipient sound and pressure waves, said twolast-named means creating air circulation throughsaidmuiliing chem r 12.A heater or the class described, comprisingacasinghavingoneendadsptedtobeconnected to a source of air supply, meansforming a combustion chamber located in said casing, a tubular heatexchanger having one end connected to said chamber and receivingproducts of combustion therefrom, a pipe extending through saidcombustion chamber and heat ex-- changer, a shell surrounding said pipeand cooperating therewith to provide a mulling chamher, said shellcooperating with said heat exchanger to form a passage for said productsof combustion, means providing openings connecting said pipe with saidchamber, means provid-v ing openings connecting said chamber with saidgas passage, said two last-named means creating air circulation throughsaid mulling chamber, a carburetor for supplying combustible mixture tosaid combustion chamber, and a connection between said pipe and saidcarburetor.

v 13. A heater 0! the class described, comprising a casing of generallycylindical cross section and having an end adapted to be connected to asource 0! air supply, means forming a combustion chamber located in saidcasing, a tubular heat exchanger having one end connected to saidcombustion chamber and receiving hot products of combustion therefrom, amuiiier shell located in said heat exchanger and cooperating therewithto form a gas passage for said products of combustion, said shell havinga tapered end adiacent said combustion chamber, a. conduit extendingthrough said combustion chamber and muiiier shell and cooperatingtherewith to form a casing of generally cylindrical cross section andhaving an end adapted to be connected to a source or air supply, meansforming a combustion chamber located in said casing, a tubular heatexchanger having one end connected to said combustion chamber andreceiving hot products of combustion therefrom, a muflier shell locatedin said heat exchanger and cooperating therewith to form a gas passagefor said products 01' combustion, said shell having a tapered end ad-.iacent said combustion chamber, a conduit extending through saidcombustion chamber and muiiier shell and cooperating therewith to form amuiiiing chamber, a single row of openings connecting said conduit withsaid mulling chamber, a row of openings in the tapered portion of saidmuiiler shell connecting said muming chamber with said gas passageway,and two rows of openings in the cylindrical portion of said muiilershell and connecting said muiiiing chamber with said mps sss m.

15. A hater of the class described, comprising a generally cylindricalcasing having an end adapted to be connected to a source of air supply,means forming a combustion chamber located in said casing, a tubularheat exchanger connected to said combustion chamber and receiving hotgases therefrom, means providing a passageway extending through saidcombustion chamber and heat exchanger, means supplying air to saidpassageway, a mui'fler shell surrounding said pipe and cooperatingtherewith to form a muiiling chamber, said mufller shell having atapered end adjacent said combustion chamber, and sound absorbingmaterial located in said muiiling chamber.

16. A heater of the class described, comprising a shell having one endadapted for connection to a source of air supply, means forming acombustion chamber located in said shell and having an end wall, atubular heat exchanger located in said shell and connected to saidcombustion chamber, a muiller located in said heat exchanger, saidmuiiier including a muilling chamber and means acoustically couplingsaid chamber to said heat exchanger and combustion chamber for dampingout incipient sound and pressure waves, and conduit means supplied withair from said source and extending through said muiiler, combustionchamber and end wall to pass cooling air therethrough to preventoverheating said muiller.

17. A heater of the class described, comprising a tubular casing havingone end adapted to be connected to a source of air supply, means forminga combustion chamber located in said casing, a tubular heat exchangerhaving one end connected to said combustion chamber receiving hot gasestherefrom, a muiiier located in said heat exchanger, said muillerincluding a muflling chamber and means acoustically coupling saidchamber to said heat exchanger and combustion chamber for damping outincipient sound and pressure waves, a cup interposed between saidcombustion chamber and muiller, said cup having a bottom locatedadjacent said combustion chamber and a top abutting a part of saidmuilier, said muilier having an extension surrounding said cup in spacedrelation thereto, said cup having perforations therein, through saidcombustion chamber and connected to said extension, means for supplyingair to said pipe, and a second pipe extending through said muffler andcommunicating with the interior of said cup.

18. A heater f the class described, comprising a tubularcasing havingone end adapted to be connected to a source of air supply, means forminga combustion chamber located in said casing, a tubular heat exchangerconnected to said combustion chamber receiving hot gases therefrom, amuiiler located in said heat exchanger, a cup interposed between saidcombustion chamber and muilier, said cup having a bottom locatedadjacent said combustion chamber and a top abutting a part of saidmuiller, said muiiier having an extension surrounding said cup in spacedrelation thereto, said cup having perforations therein, a pipe extendingthrough said combustion chamber and connected to said extension, meansfor supplying air to said pipe, a second pipe extending through saidmuffler and communicating with the interior of said cup, said mufllerhaving a muilling chamber, and sound absorbing material located in saidchamber.

19. A heater of the class described, comprising a pipeextendingatubularcasinghavingoneendadaptedtobe connected to a source ofair supply, means forming a combustion chamber located in said casing, atubular heat exchanger connected to said combustion chamber receivinghot gases therefrom, a muilier located in said heat' exchanger, a cupinterposed between said combustion chamber and mumer, said cup having abottom located adjacent said combustion chamber and a top abutting apart ofsaidmumer, said muiiier having an extension surrounding said cupin spaced relation thereto, said cup having perforations therein, a pipeextending through said combustion chamber and connected to saidextension, means for supplying air to said pipe, a second pipe extendingthrough said muilier and communicating with the interior of said cup,said munler having a single muilling compartment, and a single row ofopenings adjacent said cup and connecting said muming chamber with gaspassages between said muiller and said heat exchanger.

20. A heater of the class described, comprising a tubular casing havingone end adapted to be connected to a source of air supply, means forminga combustion chamber located in said casing, a tubular heat exchangerconnected to said combustion chamber receiving hot gases therefrom, amuiller located in said heat exchanger, said muiller including a mullingchamber and means acoustically coupling said chamber to said heatexchanger and combustion chamber for damping out incipient sound andpressure waves, a cup interposed between said combustion chamber andmumer, said cup having a bottom located adjacent said combustion chamberand a top abutting a part of said muiller, said muiller having anextension surrounding said cup in spaced relation thereto, said cuphaving perforationstherein, a pipe extending through said combustionchamber and connected to said extension, means for supplying air to saidpipe, and a second pipe extending through said mufller and communicatingwith the interior of said cup, said last-named pipe dischar in into saidfirst-named casing.

21. A heater of the class described, comprising a tubular casing havingone end adapted to be connected to a source of air supp y. means forminga combustion chamber located in said casing,

' a tubular heat exchanger connected to said combustion chamberreceiving hot gases therefrom, a muiller located in said heat exchanger,a cup interposed between said combustion chamber and muiller, said cuphaving a bottom located adjacent said combustion chamber and a topabutting a part of said muiller, said muiller having an extensionsurrounding said cup in spaced relation thereto, said cup havingperforations therein, a pipe extending through said combustion chamberand connected to said extension, means for supplying air to said pipe. asecond pipe extending through said muiller and communicating with theinterior of said cup, said last-named pipe discharging into saidfirst-named casing, a carburetor for supplying combustible mixture tosaid combustion chamber, and an inlet pipe for said carburetor, saidinlet pipe communicating with said casing adjacent the end of said heatexchanger remote from said combustion chamber.

22, A heater of the class described, comprising a tubular casing havingone end adapted for connection to a source of air supply, means forminga combustion chamber located in said casing, a tubular heat exchangerconnected to said combustion chamber, a cylindrical muiller located insaid heat exchanger and cooperating therewith amass? to form a gaspassage for hot products oi combustion from said combustion chamber,said mutfier having a large muming chamber, means for introducing airinto the end or said muming chamber which is closest to said combustionchamber, means for discharging air from the other end of said munlingchamber, and acoustic coupling means for discharging a small amount ofair from the inlet end of said mufliing chamber into said gas passagewayand for acoustically coupling said muiiiing chamber to said heatexchanger and combustion chamber for damping out incipient sound andpressure waves.

23. A heater of the class described, comprising a tubular'casing havingone end adapted for connection to a source of air supply, means forminga combustion chamber located in said casing, a tubular heat exchangerconnected to said combustion chamber, a cylindrical muiiler located insaid heat exchanger and cooperating therewith to form a gas passage,said muiiier having a, single large muiiier chamber and meansacoustically coupling said chamber to said heat exchanger and combustionchamber for damping out incipient sound and pressure waves, said muiilerhaving an end adjacent said combustion chamber, said heat exchangerhaving an and remote from said combustion chamber, means for conductingair from said remote end oi the heat exchanger to said end of themuiliing chamber, and means for discharging air from the opposite end ofsaid muiiiing chamber.

24. A heater oi the class described, comprising a tubular casing havingan inlet end and an outlet end, means forming a combustion chamberlocated in said casing adjacent said inlet end, a tubular heat exchangerlocated in said casing intermediate the ends thereof and connected tosaid combustion chamber, a muilier located in a said heat exchanger andcooperating therewith to form a gas passageway for hot products 01'combustion from said combustion chamber, said muiiler having asound-absorbing chamber and a sheet metal end located adjacent saidcombustion chamber, a pipe for conducting air from the outlet end ofsaid casing to a point adjacent said muiiier end and discharging saidair against said end, and an opening connecting said end of the mumerwith said gas passageway, said opening being of such size as toconstitute an acoustic coupling between said muiiiing chamber and saidheat exchanger and combustion chamber for damping out incipient soundand pressure waves.

25. A heater or the class described, comprising a casing having an inletend and an outlet end,

means forming a chamber located in saidcasingaheatexchangerlocatedinsaidcasing and connected to said combustion chamber, a mufler located insaid heat exchanger and having an end adjacent said combustion chamber,said muiller providing a single large acoustic chamber, means forconducting air into said mu!- nln cnamberanditss i t e or said muilieradjacent said combustion chamber, a carburetor for supplying a,combustible mixture to said combustion chamber, and means for conductingair Iran the other end of said combustion chambertosaid carburetor.

26. A heater of the class described, comprisingacasinghavinganinletendandanoutletend, means forming a combustionchamber located in said naming. a tubular heat exchanger located in saidcasing and connected to said combustion chamber, a muiller having asound-absorbing chamber and one end adjacent said combustion chamber,and means for cooling said muiiier, said means comprising a ripe forconducting air into said mumer, said pipe extending lengthwise oi saidmuiiler and scharging adjacent said end thereof, penings adjacent saidend of the muiller for connecting the interior thereof with saidcombustion chamber, said openings being of such size as to constitute anacoustic coupling between said sound-absorbing chamber and said heatexchanger and combustion chamber for damping out incipient sound andprasure waves, and an air outlet for the other end 01' said musler.

HENRY J. D! N. HOCOLLUIL REFERENCES CITED'lheiollowingrelerencesareotreeordinthe flleotthispatent:

UNIT!) STATE PA'IINTB

